1. Field of the Invention
The present invention relates to a press-formed, metal coupling element particularly suitable for use in a slide fastener which can be opened and closed in the forward direction and in the reverse direction by a pair of sliders mounted in either face-to-face or tail-to-tail confrontation on a pair of rows of discrete coupling elements, and a method of making such slide-fastener coupling element.
2. Description of the Prior Art
One known press-formed, metal coupling element for bidirectionally openable slide fasteners is disclosed in Japanese Utility Model Publication No. 1-22505. The disclosed coupling element includes a beveled side wall formed by pressing or stamping the front end of a coupling head portion. The beveled side wall generally slopes down from a protrusion side toward a pocket side of the coupling element so that the front end of each coupling element does not interfere with a protrusion of the opposite coupling element when the slide fastener is closed in the reverse direction.
The known coupling element may be made by a method or process disclosed in Japanese Patent Publication No. 63-6295 in which a metal wire that has been preformed into a Y profile is sliced into blank pieces which will become individual coupling elements, then a sliced blank piece is pushed into a head-forming station on a heading die where a protrusion and a corresponding pocket are formed by reciprocating a pocket punch toward the heading die. To transfer the blank piece into the head-forming station, a ram having a cutoff die and a cutoff punch are relatively moved with each other. Using this relative movement, the upper edge of the Y-shaped metal wire is partly compressed by a shaping shoulder of the cutoff punch so as to form a round corner edge which will extend around a pocket of the finished coupling element.
Since the beveled side wall of the known press-formed, metal coupling element slopes down from the pocket side toward the protrusion side, the opposed coupling elements are freely slidable in a perpendicular direction relative to the plane of engagement (viz. the plane of the slide fastener) immediately before they are engaged. In addition, since a guide channel formed in the slider has a height somewhat larger than the thickness of the individual coupling elements, the coupling elements of the construction previously mentioned tend to wobble within the slider. As a result. the coupling elements are coupled or interengaged insufficiently, and the movement of the sliders becomes sluggish and requires some muscle effort.